1. Field of the Invention
The present invention relates to a lightweight, quick change, derailleur gear sub-assembly for a bicycle.
2. Description of the Prior Art
Bicycle racing enthusiasts have two prime considerations when purchasing a bicycle, namely, weight and the ability of the bicycle to be rapidly repaired in the event of a breakdown in the middle of a race. The gear shift mechanism of such racing bicycles is of prime interest since known shift mechanisms are relatively heavy, susceptible of failure, and difficult to strip and repair in the field.
Specifically, one popular gear shift system, known as a "derailleur" system, comprises a plurality of chain sprockets of varying pitch diameter that are orientated in a coaxial, axially spaced conical array, a mechanism that alters the direction of movement of the chain thereby causing the chain to jump from one sprocket to another, and a spring biased idler gear that maintains a predetermined tension on the chain.
While the multiple speeds provided by such derailleur gear systems render them attractive, the weight of their gear sub-assembly and lack of rapid repair capability has heretofore presented a negative aspect to their use. This problem was partially addressed in U.S. Pat. No. 5,194,051 which discloses a gear mounting hub having a plurality of integral multistep gear support arms extending radially outwardly and axially therefrom. However, the cantilevered gear support arms and integral hub are, of necessity, relatively heavy. In addition, field strip and repair is time consuming and relatively difficult since the gears are secured to their support by conventional fasteners.